1. Field of the Invention
This invention relates to a ball spline in which a slider is formed so that the slider can be slid via balls relatively to a ball spline shaft having longitudinally extending raceway grooves.
2. Description of the Prior Art
A ball spline adapted to moving a slider linearly along a ball spline shaft via balls held and rolling in retainers has been applied to an industrial robot and a transfer machine. A ball spline constitutes a linear motion guide bearing, and comprises an elongated ball spline shaft, and a slider freely slidable with respect to the ball spline shaft and adapted to receive rotary torque from the same.
A linear motion guide ball bearing is known as a retainer-carrying ball spline. This linear motion guide ball bearing comprises mainly an outer cylinder, retainers, balls as rolling elements, and snap rings. On the outer circumferential side of the retainers, circuit type circulating passages for circulating and guiding the balls are formed. An inner circumferential surface of the outer cylinder is provided with raceways on which the balls receiving a load roll, inclined surfaces for circulating the balls smoothly from the raceways to no-load escape sections, and ball return passage-forming circumferentially inclined curved surfaces (refer to, for example, Japanese Patent Laid-Open No. 187112/1984).
A ball retainer for linear bearings, comprising a retainer body, and an annuler member adjacent to the retainer body is known as a ball spline. This ball retainer for linear bearings is formed of a retainer body and an annular piece, the retainer body being provided with loaded ball guide grooves in ball rolling regions of raceways, the annular piece being provided with semicircular recesses, which are opposed to ball turning grooves formed at an end portion of the retainer body, for smoothly carrying out the circulating and guiding of the balls (refer to, for example, Japanese Utility Model Registration No. 2504812).
The ball spline disclosed in Japanese Patent Laid-Open No. 208469/1995 filed by the applicant of the present invention has a one-piece retainer fitted in an outer cylinder body and side rings, and end seals at both ends of the retainer. This ball spline need not be provided with ball retaining claws in the outer cylinder body, and the retainer can be positioned accurately in the axial and circumferential directions with respect to the outer cylinder body. The ball spline is provided with an axial slide stop and a rotation stop on the retainer. When the retainer turned during the assembling of the ball spline, until the axial slide stop has been brought into slide contact with both of the end surfaces of the outer cylinder body with the rotation stop having contacted a rotation stop surface of the outer cylinder body, the axial and circumferential positioning of the retainer with respect to the outer cylinder is attained. When the projections of the side rings are fitted in hollow spaces between outer surfaces of projecting portions of this ball spline and wall surfaces of recessed portions of the outer cylinder body, the retainer can be fixed with respect to the outer cylinder body.
In various types of ball splines described above, escape sections comprising inclined grooves are formed at both of axial ends of raceway grooves in ball loading regions of the outer cylinder so as to guide the balls moving in direction changing passages in the retainer. Therefore, it is difficult to form the raceway grooves, and the manufacturing cost increases. Regarding the outer cylinder, to which a retainer is fixed, in a conventional ball spline, the broaching thereof and the high-precision finishing of the raceway grooves thus formed in the outer cylinder are difficult to implement, and it is also troublesome to form retainer fixing portions on the outer cylinder. This causes the outer cylinder manufacturing cost to increase.